Fuel Pressure Regulator

Fuel pressure regulator maintains a constant pressure differential for the fuel injectors. Pressure is set by the internal spring tension (approximately 2.5-3.5 bar). The lower chamber is sealed off by a diaphragm. It is connected to a manifold vacuum hose. Intake manifold vacuum influences the pressure compensation to ensure pressure differential across the injectors remains constant. The internal valve (restriction) returns the unused fuel back to the fuel tank via the fuel return line.

Fuel pressure regulator at wide open throttle has depleted manifold vacuum at the tip of the injector (and also in the vacuum chamber of the pressure regulator), therefore the pressure behind the injector is increased due to the lack of vacuum aiding the opening of the diaphragm in the pressure regulator. The spring closes the restriction to raise the pressure. Part throttle has manifold vacuum available at the tip of the injector to help flow the fuel through. That same vacuum is supplied to the pressure regulator, compensating restriction to raise the pressure.